The present invention relates generally to a composite check valve and positively closing valve, and more particularly to such a valve for regulating the introduction of secondary air into the exhaust stream of an internal combustion engine at selected times during the operation of the engine.
An internal combustion engine, particularly an automobile engine, typically is equipped with a catalytic converter to oxidize unburned hydrocarbons in the exhaust and carry out other reactions which improve the composition of the exhaust before it is discharged into the atmosphere. The catalytic converter works best if the concentration of hydrocarbons and other materials in the exhaust is not too great and adequate oxygen is provided.
When the engine is started, particularly when it is started cold, the fuel delivered to the engine is rich, and combustion is less efficient than when the engine is warm. These conditions result in a relatively high concentration of hydrocarbons in the exhaust delivered to the catalytic converter. At the same time, the oxygen in the exhaust gas is even more deficient than normal. As a result, the catalytic converter does not efficiently oxidize the hydrocarbons in the exhaust when the engine is cold. The fact that the catalytic converter itself has not reached its operating temperature aggravates this problem.
When the engine warms up, the fuel delivered to the engine is leaner and is burned more efficiently, the exhaust contains more oxygen, and the catalytic converter is at its operating temperature. As a result, the catalytic converter can function more efficiently.
The hydrocarbon-rich, oxygen-deficient exhaust of a cold engine can be catalyzed more efficiently if the exhaust gas is temporarily mixed with an oxidizing gas, typically ambient air. A secondary air supply system provides this air. In the known secondary air supply system, the outlet of an ambient air pump is connected to the exhaust via a supply valve and a check valve connected in series.
The pump operates and the supply valve and check valve pass air into the exhaust during a short interval after the engine is started, such as about two minutes. The interval is conveniently timed by an on-board computer which responds to the operation of the ignition switch. At the end of the predetermined interval, the pump is shut off. At about the same time, the supply valve is closed to isolate the pump from the exhaust system until secondary air is needed again.
The check valve prevents the reverse flow of exhaust into the supply valve and air pump while the supply valve is open. Exhaust system blockage, backfiring, or other unusual conditions could cause such reverse flow, in the absence of the check valve.
FIG. 1 shows an engine equipped with an air injection system according to the prior art. The system generally indicated at 10 comprises an intake manifold 12, feeding an engine 14, which has an exhaust manifold and an exhaust pipe at 16. The pipe 16 feeds exhaust to an air injection joint 18. A run 20 of the exhaust pipe connects the joint 18 to a catalytic converter 22.
The system for injecting secondary air at the joint 18 to supplement the exhaust stream comprises an air pump 24 having an outlet line 26 connected to the inlet port 28 of a supply valve 30. The valve 30 has an outlet port 32 connected to the inlet port 34 of a flap valve 36, which in turn has an outlet port 38 feeding the air injection joint 18 with air. The supply valve 30 and flap valve 36 are separate parts having independent housings in the prior art. The air pump 24 is turned on and off by the computer 40 via the signal line 41.
The supply valve 30 is a conventional poppet valve having a disk 42 engaging a seat 44 and a stem 46 with an opposite or downstream end 48. The stem 46 is slidable along its axis to seat or unseat the disk 42 on the seat 44. The end 48 is positioned and moved by the diaphragm actuator 50 to open or close the valve 30.
The diaphragm actuator 50 comprises an upper chamber 52 defined by the upper housing 54 and a lower chamber 56 defined by the lower housing 58. The upper and lower chambers 52 and 56 are separated by a diaphragm 60. The diaphragm 60 includes a rigid plate 62 which is fixed to the end 48. The spring 64 bears between and is located by the plate 62 and the upper housing 54. The lower chamber 56 is always vented to ambient air. The upper chamber 52 has a control port 65 receiving a vacuum line 66 which passes, via the solenoid valve 68, to the intake manifold 12--a conventional source of vacuum. The valve 68 is operated by the solenoid 70, which in turn is controlled by the computer 40.
The flap valve 36 has an apertured web 72 defining a seat and an annular, flexible flap 74 attached at its center by the button 76 to the web 72. When the flap 74 is closed, as illustrated in FIG. 1, it covers the apertures such as 78 of the seat 72. When the flap 74 opens, responsive to a greater pressure in the inlet port 34 than in the outlet port 38, it deforms so its outer edge 80 moves axially away from the web 72, uncovering the apertures such as 78 and thus permitting flow. The flap 74 is protected against buffeting and excessive deformation by a flap retaining cone 82, also secured by the center button 76 to the web 72. The flap is lightly loaded by a spring 83 bearing between the cone 82 and the flap 74 to nominally close the flap 74 and control its deformation during opening. The valve opens or closes automatically, and permits air from the pump 24 to flow into the joint 18 while preventing reverse flow of the exhaust.
The conventional air injection system of FIG. 1 works as follows. When the engine 14 is started, the computer 40 starts the air pump 24 and signals the solenoid 70 to open the valve 68. The open valve 68 permits the intake manifold 12 to draw a partial vacuum in the upper chamber 52, raising the plate 62 of the diaphragm 60 against the bias of the spring 64, thus raising the stem 46 and disk 42 of the supply valve 30 away from the seat 44 and opening the valve 30. Air from the pump 24 thus traverses the supply valve 30, forces the flap 74 away from its seat 72, and passes via the apertures 78 into the outlet port 38 and into the air injection joint 18 where it mixes with the exhaust proceeding from the engine 14 via the exhaust pipe 16. The combined air and exhaust then proceed via the run 20 into and through the catalytic converter 22.
At the end of a predetermined interval of time following operation of the ignition switch, when the engine 14 is warm and operating on a lean fuel mixture, the computer 40 signals the solenoid 70 to shift the valve 68 to isolate the intake manifold 12 from the line 66 and vent the line 66 to ambient pressure. This equalizes the pressure in the upper and lower chambers 52 and 56, allowing the spring 64 to force the plate 62, stem 46, and disk 42 toward the seat 44, thus closing the valve 30. The computer 40 also directs the air pump 24 to shut down at about the same time. The poppet valve 30 is oriented so it closes contrary to the direction of flow of the pump 24 in this embodiment so exhaust gas is doubly prevented from entering the line 26 by the valves 30 and 36.
One problem with this prior art arrangement is that it requires a supply valve 30 and an independent check valve 36 to regulate the injection of secondary air and prevent the backflow of exhaust gas. Two valves cost more and are larger than a single valve. Another possible disadvantage is that the surface of the resilient flap 74 opposite the side facing the web 72 is directly exposed hot, dirty, chemically active exhaust gases after the engine is warm and secondary air injection ceases. The flap 74 must thus be made of material which can function for an extended time in such an environment.
Failure of the flap 74 and the resulting exposure of the supply valve 30 and air pump 24 to corrosive exhaust gases, and perhaps even a consequent failure of the supply valve 30 and the pump 24, might not be readily apparent or of concern to the operator of the engine. This failure would only be detected by measuring the effluent of the catalytic converter 22 or by disassembling or inspecting the valve 30 and pump 24, so it is important that the flap 74 be a very long-lasting part in its harsh environment.